The invention relates to a pneumatic actuator for the braking system of a vehicle.
Pneumatic actuators of this type are often constructed as spring-type brake cylinders comprising a rear cylinder in which a rear piston is displaceably arranged. One side of the rear piston and the inner wall of the rear cylinder form a rear ventilation chamber. A preloaded spring, which can be compressed by the rear piston, is provided on the other side of the rear piston.
The rear ventilation chamber is sealed off by an intermediate flange traversed by a sliding rod resting against the rear piston. The sliding rod can be displaced in the intermediate flange by the rear piston. A front ventilation chamber delimited by a front piston movable in a front cylinder is provided on the side of the intermediate flange situated opposite the rear ventilation chamber. An actuating rod for a brake element of the braking system of the vehicle is provided on the front side of the piston. The rear piston and the front piston are in contact with one another by means of the sliding rod such that the front piston can be displaced by the rear piston.
When the vehicle is started, the rear ventilation chamber is filled with compressed air against the pressure of the preloaded spring so that the rear piston moves into the rear cylinder. The sliding rod also moves towards the rear in the intermediate flange and therefore no longer acts on the front piston. The front piston and the actuating rod can, therefore, also move toward the rear into the front cylinder, thereby releasing the brake element of the braking system. The vehicle therefore moves from a state in which it is braked by the preloaded spring to a non-braked state. If compressed air is admitted to the front ventilation chamber, the front piston can be moved in the front cylinder, as a result of which the brake element of the braking system can be acted upon by way of the actuating rod. Braking of the vehicle can thus be effected in a selective manner.
In the event of the failure of the compressed-air supply of the vehicle, the pressure of the compressed air in the rear ventilation chamber decreases. The preloaded spring then pushes the rear piston back into the starting position, the sliding rod acting on the front piston. The front piston in turn displaces the actuating rod such that the brake element of the braking system is actuated.
The above-mentioned embodiment results in a fail-safe operation of the vehicle.
The pneumatic actuators known in the prior art have a complicated design and can only be produced with difficulty. Sealing problems furthermore often occur, particularly if the pistons used have flexible membranes.
It is therefore an aim of the invention to provide an improved pneumatic actuator which can be produced in a simple manner.
According to one of the ideas underlying the invention, the intermediate flange is received in the interior of the rear cylinder or in the interior of the front cylinder. The front cylinder is fixed to the rear cylinder. This design results in considerable advantages over the pneumatic actuators known in the prior art. The actuator according to the invention can first be designed to be stackable, e.g. in one step, the rear cylinder and the components therein and, in another step, the front cylinder and the corresponding components. For the final assembly, the intermediate flange then simply has to be introduced into the rear cylinder or into the front cylinder, after which the connection between the rear cylinder and the front cylinder is established.
A reliable connection between the rear cylinder and the front cylinder can be achieved by a form-locking connection, e.g. by means of a thread-type connection or by means of a connection produced by a forming step. In particular, it is contemplated for one wall of the front cylinder and one wall of the rear cylinder to be mutually connected by means of a curled region. A shoulder is advantageously provided in one of the walls of the front cylinder or the rear cylinder, over which a region of the other cylinder is curled. Particularly durable connections between the rear cylinder and the front cylinder can be produced in this manner, and a reliable connection can be established over the entire circumference of the housing of the relevant cylinder.
One particularly advantageous embodiment of the invention is produced if the front piston or the rear piston has a substantially circular disc-shaped or ring-shaped flexible membrane connected in the region of its outer edge to the wall of the front cylinder or of the rear cylinder. In this embodiment of the relevant piston, the membrane edge is enclosed between the wall of the cylinder and the intermediate flange. A connection of this kind can be produced in a particularly simple and reliable manner by means of the pneumatic actuator according to the invention. Unlike the pneumatic actuators known in the prior art, the pneumatic actuator according to the invention can be finished and sealed in a simple manner in one step. By virtue of the fact that the wall of the rear cylinder is joined to the wall of the front cylinder, any membrane provided can be installed in a simple and particularly reliable manner, with particularly good sealing being achieved.
The production method according to the invention provides that the front cylinder is connected to the rear cylinder in a final step, wherein the front cylinder can be fixed to the rear cylinder by welding, screwing, soldering, curling and/or clamping with a sleeve.
The invention will be described in more detail by way of three embodiments illustrated in the drawings.